Dental implant comprising an anchoring head and a screw element

ABSTRACT

A set of dental implants comprising two implants each having an anchoring head for a structural element and having an end face of a predetermined face diameter and a screw element with a thread core and a self-cutting outer thread. The thread core and the outer thread have three segments following one another in succession from crestal to apical, namely a crestal segment adjoining the anchoring head with a constant outer crestal diameter of the outer thread and a thread core conically tapering in the apical direction to a predetermined intermediate diameter, a middle segment with an outer diameter of the thread core substantially equal to the intermediate diameter, and a tip segment with an outer thread of an outer diameter tapering in the apical direction and a conically tapering diameter of the thread core. The face diameters of the two implants are different.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national phase of PCT applicationPCT/EP2003/007288, filed 8 Jul. 2003, published 12 Feb. 2004 as WO2004/012622, and claiming the priority of German patent application10234113.3 itself filed 26 Jul. 2002 and German patent application10238091.0 itself filed 21 Aug. 2002.

FIELD OF THE INVENTION

The invention relates to a dental implant with an anchoring head for astructural part and a screw element comprising a threaded core and aself-cutting outer screw thread. The invention also relates to a set ofdental implants and to a final drill for creating the finished bore toreceive such a dental implant.

BACKGROUND OF THE INVENTION

Screw thread configurations for the screw element of dental implants areknown from a number of publications in the state of the art. Thus DE 20113 254 U1 describes a cylindrical screw implant in which, starting froma cylindrical anchoring head, the screw thread core conically tapered indiameter from crestal to apical while the self-cutting outer screwthread has a constant outer diameter over its length. Because of thefact that the thread becomes increasingly deeper from apical to crestal,at the apical end the implanted screw element forms gaps between theinner wall of the cylindrical final bore in the jaw bone and the threadcore which is detrimental on medical grounds.

With the shape of the screw element known from DE 37 35 378 C2, thescrew thread has an outer diameter which is constant over the greaterpart of its length for the thread core and outer thread portion. Onlytoward the apical end of the screw element does the thread core andouter thread have a slightly conical configuration. Because the greaterpart of the thread length has a constant outer diameter, this earlierdental implant upon screwing requires relatively greater force withincreasing depth to which the implant is screwed into the jaw bone whichcan result in a relatively strong trauma to the impacted bone tissue.

DE 36 42 901 A1 discloses a special thread for a dental implant whichhas a relatively strongly conically tapered thread core combined with anouter thread up to a short conical run to the apical end with a constantouter diameter. Here as well the problem arises in that the greatestthread depth is in the region ahead of the apical end.

EP 0 282 789 B1, finally relates to a self-cutting bone implant fordental purposes which can be screwed into the bone and which has athread configuration which corresponds to that of the first mentionedutility model. To the extent that also combines a conically taperedthread core with an outer thread whose outer diameter is constant, theouter diameter especially is equal to the outer diameter of thecylindrical post anchor.

As further alternatives for the screw element, a screw pattern isclaimed in this publication whereby the outer diameter of the outerthread which is equal to the diameter of the cylindrical anchoring head,constantly is reduced toward the free end of the core and a conicalthread core is provided. In other words, a conically tapering outerthread is combined with a core which is also conical. As a result of thecontinuous diameter reduction and the omission of any cylindricalsegments in the thread core and/or outer thread, the stability andintrinsic bond between the implant and surrounding bone tissue can beaffected.

As can be deduced from the state of the art represented by thepublication but not explicit therefrom but known from the actualpractice employing dental implants, the bores provided in the jaw bonein all cases have diameters such that the outermost tips of the screwthread rib will penetrate into the bone tissue. The thread turns can bethen formed as recesses which grow to stabilize the seat of the implantin the bone tissue. It is desirable to improve such dental implants,especially as to their primary stabilities.

OBJECT OF THE INVENTION

The invention has as its object, starting from the problem of the stateof the art to be attacked, to so improve a dental implant with respectto the screw element that the greatest possible stability of theanchoring with the smallest possible stress upon the bone regionsurrounding the implant can be produced.

SUMMARY OF THE INVENTION

This object is achieved by the instant invention in that the thread coreand the outer thread have three segments in succession from the crestalto the apical, namely, a crestal segment connected to the anchoring headwith a constant outer diameter of the outer thread and, in the apicaldirection, a conical thread core, an intermediate segment with basicallyconstant outer diameter of the outer thread with a constant diameter fothe thread core, and a tip segment with a conical outer diameter of theouter thread in the apical direction and constant diameter of the threadcore.

Thus cylindrical and conical thread patterns are used both in the threadcore and also in the outer thread, to form a combination withoptimization of the function of the individual thread segments. In thismanner in the apical point segment there is a continuous increase in thecutting cross section and the core diameter to produce a clean cut intothe bone of the respective counter thread. The middle segment haspractically a cylindrical thread portion without conical or otherwisecontinuously reducing patterns of the thread core or the outer thread toprovide good stability with however a simultaneous balanced loading ofthe surrounding material by the uniform pressing over its entire area ofthe screw thread rib. Finally the crestal segment serves to provide aclean transition from the screws body to the anchoring head so that inthis region sharp edges and corresponding stress concentration as wellas notch effects or sudden changes in the bond tissue are avoided.

This is especially the case when, as in a preferred embodiment isprovided, the crestal segment transitions steplessly with its conicalthread core into the anchoring head. Upon the implant insertion, theimproved thread configuration enables an ideal anchoring in the bone sothat an optimal primary stability can be achieved with all bonedensities. This primary stability can be enhanced by a subtractivesurface area enlargement. By contrast with additive surface arearoughening, as is the case with particle coatings, the detrimental shearwhich is applied by such parts, especially titanium particles,especially with self-cutting threads during insertion, is reduced.Preferably the outer thread of the screw element is configured as adouble thread which enables a cleaner insertion of the implant as lessbone deterioration. The result is a reduced healing time for theimplant.

According to a further preferred embodiment, the ratio of the axiallengths of the crestal or tip [point] segment on the one hand to themiddle segment on the other is between about 1:1 to 1:2. Depending uponthe respective diameter of the dental implant, with this ratio theanchoring and screw setting characteristics described at the outset canbe produced. The same goal is served with a preferred ratio of thethread outer diameter in the crestal and middle segments of the apicalend of the point or tip segment of about 4:3.

To anchor the respective structural part [crown] according to a furtherpreferred embodiment of the invention, on the anchoring head there is ahexagonal rounded tooth socket, a so-called Torx® socket which, bycontrast to hexagonal straight tooth arrangements of the Allen-typebecause of their rounded-force engagement surfaces parallel to the screwaxis, have a significantly reduced pressure upon the engaged area andthereby less danger of damaging the insertion tool and the structure tobe mounted upon the implant. In this manner the implant is able toabsorb all of the forces transmitted to it with a high degree ofreliability. In addition rounded hexagonal teeth by comparison withplanar hexagonal teeth for a given fabrication tolerance can have asignificantly better torsional reliability, i.e. security againstrelative rotation of the interconnected parts.

In addition with a hexagonal socket with its angle of attack of 60° ateach individual tooth a greater part of the torque is converted intoradial forces which act against the surfaces of the socket and do notparticipate in the screwing-in force which may be required. The internalhexagonal rounded toothing thus as a whole facilitates the driving ofthe implant more readily into the bone and provides a correspondinghighly stable anchoring against rotation of the structure [crown] whichis engaged in the internal teeth.

According to a preferred embodiment of the invention a set of dentalimplants is provided in which the crestal anchoring surface for theanchoring head and onto which the structure is to be affixed, can haveone with a normal outer diameter and two different dental implants withouter diameters which differ. This set configuration is advantageouswith such dental implants which may not have the characterizing featuresof claim 1 as to the thread configuration as well.

As an advantageous set grouping, there can be a three member set havingimplants in the form of a normal thread implant, a small thread implantand a wide thread implant, whereby in the region of the cylindricalanchoring head all three implant diameters can meet the common normalouter diameter of the anchoring head. This has the significant advantagethat one and the same structural components can be used for threedifferent implant diameters without requiring the structural componentsto be mounted to have stepped diameters, sharp back or front projectionsor the like between the component to be mounted and the anchoring head.In implant practice, the cost of storage and stocking for the structuralcomponents to be affixed to the implant can be reduced corresponding tothe number required for a set by the number of implants in the set, hereby one-third. With the implant system of the invention by comparisonwith known implant systems having multiple structural components to bemounted and implants for mounting them, the number can be drasticallyreduced and significantly limited.

Finally the invention provides a final drill for producing the finalbore to receive a dental implant and which has a conical cutting contourwith a conical angle matched to the conical pattern of the thread coreand an outer diameter matched to the outer diameter of the screw thread.Because of the conical form the dental implant can be set in the jawsuch that before the screwing process begins, it will adopt especiallywell its desired orientation and can then be screwed in substantiallyespecially free from wobbling. In the final screwing into place, thethread rib of the outer thread cuts increasingly into the bone tissue sothat the screw thread is initially filled. This achieves a high primarystability.

BRIEF DESCRIPTION OF THE DRAWING

Further features, advantages and details of the invention are given inthe following description in which an embodiment is described in greaterdetail in conjunction with the accompanying drawing. It shows:

FIG. 1 a longitudinal axial section through a dental implant,

FIG. 2 a cross section through the dental implant along section lineII—II of FIG. 1,

FIG. 3 a section through the dental implant according to section lineIII—III of FIG. 1,

FIG. 4 a side view of the dental implant of FIG. 1 as a normal threadimplant,

FIG. 5 a side view of a small thread implant,

FIG. 6 a side view of a wide thread implant, and

FIG. 7 a schematic side view of a final drill.

SPECIFIC DESCRIPTION

As will be clear from FIGS. 1, 3 and 4, a dental implant 1 has ananchoring head 2 which in its outer contour is rigorously cylindricaland formed in one piece with a screw element 3 extending in an apicaldirection. The anchoring head 2 has a crestal anchoring area 4 which iscoaxial with the longitudinal axis L and is formed with an internalhexagonal set of rounded teeth 5 which serve for engagement in a formfitting manner with an implanting tool or element capable of rotatablydriving the implant and for the engagement with the end which can beplugged into the implant of a superstructure 15 or other element to bemounted thereon (FIGS. 4 to 6). The internal teeth 5 terminate in theapical direction at a blind bore 6 with an internal screw thread 7 intowhich the anchoring screw of the superstructure 15 can be threaded tomount the structure on the implant 1. While the internal teeth 5 extendsubstantially over the entire length of the anchoring head 2, the blindbore 6 occupies about ⅓; of the length of the screw element 3.

As can be seen especially from FIG. 1, the screw element 3 has a threadcore 8 and a self cutting external thread 9. In the direction of thelongitudinal axis L, the thread core 8 and the outer thread 9 aresubdivided into three segments 10, 12, and 13 following one another fromthe crestal to the apical, and of which the first crestal segment 10adjoins the anchoring head 2. In this segment the outer thread 9 has aconstant outer diameter D₉ of for example 4.5 mm which corresponds tothe outer diameter of the anchoring head 2. The thread core 8 runs inthis segment 10 conically tapering in the apical direction anddiminishes from a diameter corresponding to the diameter D₉. The threadcore 8 thus merges steplessly into the outer surface of the anchoringhead 2. The diameter reduction of the thread core 8 in the segment 10continues to an intermediate diameter D₁₁ which for example is of theorder of close to a half millimeter less than the outer diameter D₉ ofthe anchoring head 2.

The middle segment 12 adjoins the crestal segment 10 and in this middlesegment 12 the outer diameter D₁₂ of the outer thread 9 and the outerdiameter D₁₁ of the core 8 remain constant. The apparent reduction ofthe outer diameter in the middle segment is a result of the longitudinalgrooves 14 shown in the section of FIG. 1 and described further below.

In the third point or tip segment 13 both the outer thread 9 and thethread core 8 conically taper in the apical direction to a diameter D₁₃or

D₁₄, respectively. The thread outer diameter D₁₃ amounts there, forexample, to about 3.5 mm.

To make the above-described thread configuration more clear, the courseof the thread core 8 has been illustrated on one side of the section ofFIG. 1 in bold dot dash lines. On the same side, also indicated in dotdash lines, is the envelope E of the outer thread 9 at the point or tipsegment 13.

As also will be apparent from FIGS. 1 and 2, beginning at the middlesegment 12 on two diametrically opposite sides of the screw element 3,two parallel longitudinal grooves 14 are provided which run parallel tothe longitudinal axis and have lengths which amount to about ⅔ of theimplant length a.

As to the dimensioning of the lengths and diameters of the implant, inaddition to the length a=12 mm, the length L₁₀ of the crestal segment 10can amount to 2.8 mm, the length L₁₂ of the middle segment 12 can amountto about 3 mm and the length L₁₃ of the tip segment 13 can amount toabout 3.5 mm. In the case of an implant of total length a=8 mm, thelengths L₁₀ and L₁₃ of the crestal segment 10 and the tip segment 13 canbe only 1.8 mm. The crestal segment 10 and the tip segment 13 are thuseach only about half as long as the middle segment 12.

The outer thread 9 itself has a pitch of 1.8 mm and is provided in thetip segment 13 with a chamfer.

FIGS. 4 to 6 show a set of dental implants 1 (FIG. 4), 1′ (FIG. 5) and1″ (FIG. 6) whose thread configuration corresponds to that which hasbeen described above. To that extent, no further clarification isrequired for the dental implants 1′ and 1″. The dental implant 1 is thenormal thread implant 1 of the set in which the anchoring head 2 has arigorously outer configuration with a normal outer diameter D_(N)(corresponding to D₉). The anchoring area 4 correspondingly has thisnormal outer diameter D_(N). The structural part or crown 15 mounted onthis head 2, which is held in the internal tooth structure 5 againstrotation and is secured by a screw not shown traversing the part 15 andthreaded into the internal screw thread 7 has been indicated by brokenlines in FIGS. 4 to 6 and has the same normal external diameter D_(N).Thus between the part 15 and the anchoring head 2, there is a completelyflush or smooth transition.

The small thread implant 1′ shown in FIG. 5 has an outer diameter D_(S)corresponding to the outer diameter of the outer thread 9 and theanchoring head 2 and which is smaller than the normal outer diameterD_(N), in the example about 0.5 mm. For this purpose, the anchoring area4 again has a diameter corresponding to the normal diameter D_(N) whilethe anchoring head 2 has a crestal edge forming a circumferentiallywider rib like shoulder 16 whose outer diameter corresponds to thenormal diameter D_(N). The step between the anchoring head 2 and thewidening shoulder 16 is provided with an inner radius 17 formed bycoining or embossing so that no sharp undercut will be formed on thedental implant 1.

In FIG. 6, a wide thread implant 1″ has been illustrated in which theouter diameter D_(B) of the outer thread 9 at the crestal segment 10 andthus the anchoring head 2 is, for example, 0.5 mm greater than thenormal outer diameter D_(N). Here as well, a matching of the diameter ofthe anchoring surface 4 to the part 15 to be mounted thereon is requiredand for this purpose, the anchoring head 2 at its crestal edge acircumferential bevel 18 which delimits the crestal edge 19 of thenormal outer diameter D_(N). The bevel 18 forms a bevel angle 20 withthe radial plane of 60° so that here as well, a relatively smoothtransition to the mounted part 15 is obtained.

A final drill 21 which serves to form a final bore to accommodate thedental implant 1 illustrated in FIGS. 1 to 4, has been shown in FIG. 7.This final drill 21 has a conical cutting body 22 defining its outercontour and formed by 3 cutters not shown in greater detail. The latterextends from the tip 23 over the surface 24 of the drill 1 to a depthabutment [stop] 25 in the form of a circumferential shoulder. Thisprojects radially both the cutting body 22 and thus limits the drillingdepth. The pitch of the cutters not shown usually amounts to, forexample, 50 mm so that the active cutting surface of the cutting bodyreaches from the tip 23 to the abutment 25. This active coating surfacehas been indicated in FIG. 7 by the broken lines around the cutting body22. The cutting body 22 tapers toward the tip 23 uniformly and thus hasa conical cutting contour whose cone angle is matched to the conicalpattern of the cone 8 of the thread of the dental implant 1, that is theconical angle of the crestal segment 10 and the tip segment 13correspondingly, the outer diameter D_(FB) is matched to the respectiveouter diameter D₁₁, D₁₄, that is it varies within several tenths of a mmin the same magnitude.

On the opposite side of the depth abutment from the cutting body 22, thefinal drill 21 has an anchoring shaft 26 with which the drill 21 can beinserted into a corresponding hand-guided drive head for dental tools.

1. A set of dental implants comprising two implants each comprising: ananchoring head for a structural element and having an end face of apredetermined face diameter; and a screw element with a thread core anda self-cutting outer thread, the thread core and the outer thread havingthree segments following one another in succession from crestal toapical, namely a crestal segment adjoining the anchoring head with aconstant outer crestal diameter of the outer thread and a thread coreconically tapering in the apical direction to a predeterminedintermediate diameter, a middle segment with an outer diameter of thethread core substantially equal to the intermediate diameter, and a tipsegment with an outer thread of an outer diameter tapering in the apicaldirection and a conically tapering diameter of the thread core, theouter crestal diameter of one of the two implants being substantiallyequal to the face diameter and the outer diameter of the other of thetwo implants being larger or smaller than the outer crestal diameter. 2.The dental implant according to claim 1, characterized in that the outerthread is formed as a double thread.
 3. The dental implant according toclaim 1, characterized in that the ratio of the axial lengths of thecrestal segment or the tip segment on the one hand to the middle segmenton the other hand lies between 1:1 and 1:2.
 4. The dental implantaccording to claim 1, characterized in that the ratio of the threadouter diameter in the crestal segment and the middle segment to that ofthe apical end of the tip segment lies at about 4:3.5.
 5. The dentalimplant according to claim 1 characterized in that the anchoring headhas an internal hexagonal rounded surface toothed socket adjacent ablind threaded bore close to the apical side.
 6. A final drill forcreating a final bore for a dental implant according to claim 1,characterized in that the final drill has a conical cutting contour withthe conical pattern matched to the conical angle of the thread cores andwith an outer diameter which corresponds to the outer diameter of thethread cores.
 7. A final drill according to claim 6 characterized inthat the drill has multiple cutters, preferably three cutters, wherebythe cutters extend from the tip over the area of the drill up to a depthstop on the shank.